88. In many localities it is necessary to guard against dampness in cellar walls, particularly in buildings where the basement is used for living rooms or for storage. There are several devices for preventing moisture from entering the walls, one class being in the nature of applications to the outside of the wall and the other being constructive devices.
Where only surface water is to be provided against, and the ground is not generally saturated with water, coating the outside of the wall with asphalt or Portland cement will, in most cases, prove a preventative against dampness.
Asphalt, applied to the outside of the wall while boiling hot, is generally considered as the most lasting and durable of all coatings. To insure perfect protection, the wall should have been built as carefully as possible, the joints well pointed and the whole allowed to get dry before the coating is applied.
The asphalt should be applied in two or more coats and carried down to the bottom of the footings.
If the soil is wet and generally saturated with water, moisture is apt to rise in the wall by absorption from the bottom. To prevent this, two or three thicknesses of asphaltic felt, laid in hot asphalt, should be bedded on top of the footings, just below the basement floor, as shown by the heavy line, Fig. 48.
Portland cement may be used in place of asphalt if the ground is not exceeding damp, but if it is often saturated with water asphalt should be used. The objections to Portland cement are that it is easily fractured by any settlement of the walls, and being to some degree porous, suffers from the action of frost.
Common coal tar is also often used for coating cellar walls; it answers the purpose very well for a time, but gradually becomes brittle and crumbles away.
89. Of the constructive devices, the simplest is to make the excavation about 2 feet larger each way than the building, so that there will be about a foot or 10 inches between the bottom of the bank and the wall, as shown in Fig. 48. A "V-shaped tile drain should be placed at the bottom of this trench after the wall is built and connected with a horizontal drain, carried some distance from the building.
The trench should then be filled with corbels, coarse gravel and sand. If the top, for a distance of about 2 feet from the building, is covered with stone flagging or cement, it will assist greatly in keeping the walls dry.
By draining the soil in this way, and also coating the wall with asphalt or concrete, a perfectly dry wall will in most cases be insured For greater protection of the basement from dampness, the basement walls should be lined with a 4-inch brick wall with an air space between the main wall and the lining, or an area should be built all around the outside walls.